Aromatic acid chloride process

ABSTRACT

Process for preparing aromatic acid chlorides such as isophthaloyl chloride and terephthaloyl chloride, useful as intermediates for making polyester, polyamide and the like condensation polymers, which includes heating an aromatic compound containing at least one dichloromethyl group bonded to an aromatic carbon atom with a sulfur reactant (SO2, SOCl2 or mixtures thereof) and, optionally, molecular oxygen at about 200*-300* C. and at a pressure and for a time sufficient to convert at least one dichloromethyl group to a carbonyl chloride group.

United States Patent Rondestvedt, Jr.

1 51 Aug. 1, 1972 AROMATIC ACID CHLORIDE PROCESS [72] Inventor: Christian S.

Wilmington, Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Nov. 10, 1969 [21] Appl No.: 875,541

Rondestvedt, Jr.,

[52] US. Cl. ..260/544 M [51] Int. Cl ..C07c 51/58 [58] Field of Search ..260/544 M, 524 S [56] References Cited UNITED STATES PATENTS 2,928,879 3/1960 Strickland ..260/599 FOREIGN PATENTS OR APPLICATIONS 1,302,418 7/1962 France Primary Examiner-Lorraine A. Weinberger Assistant Examiner-Richard D. Kelly Attorney-Francis J Crowley l 5 7 ABSTRACT Process for preparing aromatic acid chlorides such as isophthaloyl chloride and terephthaloyl chloride, useful as intermediates for making polyester, polyamide 9 Claims, No Drawings AROMATIC ACID CHLORIDE PROCESS The subject invention relates to a process for converting dichloromethyl-benzenes to acid chlorides by reaction with sulfur dioxide, thionyl chloride or sulfur dioxide-thionyl chloride mixtures, optionally in the presence of oxygen.

BACKGROUND Aromatic acid chlorides are valuable intermediates, particularly poly-acid chlorides, such as isophthaloyl chloride and terephthaloyl chloride, useful for making polyester, polyamide and the like condensation polymers. One proposed route to acid chlorides involves perchlorinating such methyl-aromatic compounds as toluene, m-xylene, p-xylene, and mesitylene in the side chain converting the resulting trichloromethyls to carbonyl chloride groups. The side chain chlorinations are often incomplete and there are also produced dichloromethyl compounds, which cannot be directly converted to the desired acid chlorides by prior methods based on trichloromethyl chemistry.

US. Pat. No. 3,124,61 1 discloses that SO under pressure at 200 400 C. oxidizes aromatic methyl and chloromethyl (-CH Cl) side chains to carboxyl CO l-l) groups.

U.S. Pat. No. 3,41 1,886 discloses that S with FeCl catalyst, reacts with aromatic CCl compounds at temperatures up to 120 C. to yield thionyl chloride and aromatic acid chlorides.

BRIEF SUMMARY OF THE INVENTION The subject process for preparing aromatic acid chlorides in general involves heating A. an aromatic compound containing a benzal chloride moiety optionally substituted with one or more ring fluorine, chlorine, dichloromethyl (CHCl or carbonyl chloride (COCl) groups, the carbon-containing substituents being non-ortho to each other and to the benzal chloride CHCl group, with B. a sulfur reactant chosen from sulfur dioxide (S0 thionyl chloride (SOCI or mixtures thereof and, optionally,

C. molecular oxygen in a minor amount sufiicient to facilitate the conversion of dichloromethyl groups to carbonyl chloride groups, at a temperature in the range 200 to 300 C under pressure for a time sufi'rcient to convert the benzal chloride to a benzoyl chloride having at least one more COCl group than the starting benzal chloride.

DETAILED DESCRIPTION OF THE INVENTION Basis for the Invention:

This invention is based on the discovery that sulfur dioxide or thionyl chloride or the combination thereof is effective to oxidatively convert benzal chloride and various substituted benzal chlorides to the corresponding benzoyl chlorides, and that the reaction can be facilitated by small amounts of molecular oxygen. The oxygen use embodiment is particularly valuable when more than one dichloromethyl or a carbonyl chloride group is already present in the molecule.

As described in my co-pending application Ser. No. 875,533, filed concurrently herewith on Nov. 10, 1969, entitled Aromatic Acid Chloride Process, sulfur dioxide, alone or in the presence of thionyl chloride, rapidly converts benzotn'chlorides to benzoyl chlorides at 350 C. Sulfur dioxide reacts much faster with trichloromethyl (CCI3) than with CHC], so that when both groups are present in the same molecule the CCl group can be made to react substantially exclusively to produce dichloromethyl acid chlorides like a,adichloro-metatoluyl chloride.

According to the present invention, compounds like a,a-dichloro-meta-toluyl chloride can be converted to the poly-acid chloride, particularly when oxygen is employed along with the sulfur dioxide and/or thionyl chloride.

Thus whereas my above-referenced application Ser. No. 875,533 provides a method for converting poly trichloromethyl compounds like a,a,a,a,,a,a'-hexachloro-meta-xylene to isophthaloyl chloride, the present invention provides a method for converting under-chlorinated xylenes such as a,a,a',a'- tetrachloro-meta-xylene and a,a,a',a',a'-pentachlorometa-xylene to the desired isophthaloyl chloride without first having to further chlorinate the underchlorinated xylenes to the hexaehloride stage.

Another significant practical aspect of the present invention is that it is operable with CI-lCl compounds that are normally difiicult or impractical to convert to CCl compounds as acid chloride precursors. For example, side chain chlorination of 2,6-dichloro-toluene stops at the benzal chloride stage; further chlorination tends to degrade the molecule to 1,2,3-trichlorobenzene.

Similarly, when ring chloro substituents are present, it is difficult to chlorinate methyl side chains in the xylenes to the perchloro stage. The present invention obviates the need to do so and thus provides for direct conversion of the underchlorinated CHC1 groups to COCl groups.

The Dichloromethyl Component:

This component includes benzal chloride (dichloromethylbenzene) and substituted benzal chlorides containing a total of one to three dichloromethyl groups and one or more F, C], or COCl groups, provided all the carbon-containing groups (CI-ICI- and COCl) are on non-adjacent positions. In other words the combined total of CI-lCl and COCl groups equals one to three. It also includes binuclear analogs of the dichloromethylbenzenes wherein two phenyls, with one or both carrying one or more dichloromethyl groups, are joined through an electron pair bond or an alkylene group such as methylene, ethylidene, propylidene or butylidene, which is inert under the conditions of the reaction. The binuclear analogs may carry F, C1 or COCl substituents as noted above.

Representative substituted benzal chlorides are: 2- chloro-, 2,4-dichloro-, 2,6-dichloro-, pentachloro-, 2- fluoro-, 3-fluoro-, and 2,4-difluorobenzal chloride; a,a,a',a-tetrachloro-m-xylene, i.e., l ,3- bis(dichloromethyl) benzene, a,a,a,a' -tetrachloro-pxylene, a,a,a',a' ,4-penta-chlorom-xylene, a,a,a',a' ,4,5-hexachloro-m-xylene, a,a,a',a,2-pentachloro-pxylene, a,oz,a',a' ,2,5-hexachloro-p-xylene; oz,adichloro-3-toluyl chloride, i.e., m-dichloromethylbenzoyl chloride, 01,0: -dichloromethyl-4-toluyl chloride, a,a,4-trichloro-3-toluyl chloride, a,a,5-trichloro3-toluyl chloride, 01,0: ,4,5-tetrachloro-3-toluyl chloride, a,a,4,5,6-pentachloro-3-toluyl chloride, a,a,2-trichloro-4-toluyl chloride, a,a,2,5-tetrachloro- 4-toluyl chloride, S-dichloromethylisophthaloyl chloride, 3,5-bis(dichloromethyl) benzoyl chloride, pdichloromethyl-biphenyl, p,p'-bis(dichloromethyl) biphenyl, bis(p-di-chloromethylphenyl)methane, and 2,2-bis(pdichloromethyl-phenyl)propane.

The preferred dichloromethyl benzenes contain a total of two to three CI-lCl and COCl groups combined and up to three chloro groups since these yield the desired benzene polycarbonyl chlorides. Particularly preferred of this class are those containing a total of two CHCI and CDC] groups since these yield the most highly desired isophthaloyl and terephthaloyl chlorides.

As disclosed in my above-referenced application Ser. No. 875,533, trichloromethyl benzenes are precursors of benzene carbonyl chlorides. Trichloromethyl substituted benzal chlorides which correspond to carbonyl chloride-substituted benzal chlorides described above may be used to generate those carbonyl chloride-substituted benzal chlorides for use in the present process, conveniently by reaction with S in accordance with said referenced application. Such trichlorornethyl benzal chlorides include a,a,a,a',a'-pentachloro-mxylene, a,a,a',a',aflpentachloro-p-xylene, such compounds containing ring chloro-substituents, and a,a,a ,a' ,aa ,a' ,a ,a' '-octachloro-mesitylene.

The Process General:

In the broad aspect of this process, an aromatic compound containing one or more dichloromethyl groups as described above and the sulfur reactant are heated together, with and without oxygen to effect the transformation of one or more dichloromethyls to carbonyl chloride groups. The reaction stoichiometry may be represented as:

l. ArCHCl S0 (and/or SOCI 'ArCOCl products containing sulfur and chlorine, as in 50, S, sulfur chlorides and HCl.

It will be noted that in the overall reaction, the Cl-lCl group which formally corresponds to an aldehydric oxidation state has been oxidized to the higher carboxylic oxidation state, while the S0 and/or SOCl has been reduced to a lower valent state.

Equation 1 requires one S0 or SOCl molecule for each Cl-lCl group to be converted. The actual quantity employed depends on the dichloromethyl compound, the operating temperatures and pressures and the degree of contact between the reactants during reaction. The preferred sulfur reactant contains at least one 80 molecule for each CHCl group.

The temperature required for the -CHCl to -COCl conversion usually is in the 200 to 300 C. range, preferably 220 to 260 C. S0 normally boils at l0 C. and SOCl at 77 C., so that for effective contact with the dichloromethyl component at these elevated operating temperatures the reaction is generally conducted under agitation in closed vessels with at least one and usually not more than about moles of the sulfur reactant per CHCl group. Larger proportions may be used but are normally not necessary. The reactor loading is adjusted such that the sulfur reactant pressure in the free space is sufficiently great to maintain the reactant, particularly sulfur dioxide, in the phase occupied by the dichloromethyl compound. Normally pressures at the operating temperatures of at least about 200 p.s.i.g. are used, preferably at least 500 p.s.i.g., the higher the better, with pressures greater than about 5000 p.s.i.g. seldom necessary. The upper pressure limitation depends only on the ability of the equipment to withstand pressure. The means employed to agitate the reaction mass should be efiective of course to disperse the sulfur dioxide in the reaction mass and provide intimate contact among the reactants.

The sulfur reactant consumed during the reaction may be replenished by feeding additional quantities into the reactor, either into the reaction mass itself or into the free space normally present in closed systems. In one contemplated operating mode, S0 iscontinuously fed to the otherwise closed reactor during the reaction to maintain a substantially constant, high S0 partial pressure in the vapor space and thus provide a high proportion of S0 dissolved in the reaction mass liquid phase.

Where poly-acid chlorides are to be produced from benzal chlorides bearing 1 to 2 trichloromethyl groups (as in situ precursors of additional COCl groups) there is ordinarily used one to 10 additional moles of S0 per CCl present, preferably 1.1 to five moles per CCI and the reaction mixture is heated in a pre-invention process step at to 300 C., preferably 200 to 260 C., to convert the CCl groups to COCl groups. As stated earlier, the CCl groups react faster than and substantially preferentially to the CHCl groups under these conditions so that the corresponding benzal chloride is produced bearing one to two COC] groups corresponding to the original CCl groups. In accordance with this invention, the COCl-containing dichloromethyl compound is then further heated with 80, under the conditions of this invention as defined and described above. The overall process of converting CCl -substituted phenyl-CHCl compounds to benzene poly carbonyl chlorides may be conducted in the one reactor employing sufficient S0 to convert the Cl'lCl as well as the CCl groups to COCl groups.

Thionyl Chloride:

While thionyl chloride is itself operative, it is preferably employed with $0 In such mixtures SOCl provides additional advantages: It increases SO, solu bility in the reaction mixture and it scavenges water, either water originally present as contaminant or produced in situ, e.g., by reaction of oxygen with the CHCl groups. For reasons of economy, from 0.1 to two moles of SOC1 per mole S0 are used, preferably 0.2 to one mole/mole. When water is present or oxygen is employed, the SOCl quantity should be at least sufiicient to convert the water present initially or produced in the reaction to S0 and HCL. It is advantageous when employing SOCl to vent HCl gas during the reaction to avoid excess pressure strain on the reactor. Oxygen Use:

Oxygen (0 also facilitates the -CHCl to -COCl conversion, although with unsubstituted benzal chloride it tends also to promote tar-forming side reactions. 0 either as oxygen gas or air, is preferably employed with the electronegatively substituted benzal chlorides, particularly those bearing COCl groups, for example a,a-dichloro-meta-toluyl chloride and its ringchlorinated derivatives.

Although beneficial results may be obtained using from about 0.1 to 0.5 mole of oxygen per CHCI, group to be converted, the preferred amount is 0.2 to 0.4 molecule per CHCl which encompasses what is considered to be the stoichiometric 0.25/ 1 ratio, by which CHCI hydrogens and the oxygen involved are combined to form water.

Reaction Product Recovery:

For all process embodiments, after the reaction is substantially complete, the reaction mass is normally cooled, vented to recover unreacted sulfur dioxide, thionyl chloride, hydrogen chloride and other volatile products, and the mixture worked up to recover the higher boiling acid chloride, which if necessary may be distilled at reduced pressures as disclosed in British Pat. No. 946,491 and US. Pat. No. 2,856,425. Where the acid chloride is normally solid or not distillable, it may be purified if desired by crystallization from melts or from solvent as is also well known to the art.

Other Invention Features:

One feature of this invention is that reaction solvents are normally not needed. They may be used, however, and in some cases afford substantial benefits by facilitating contact between the preferred sulfur dioxide reactant and the dichloromethyl compound. Useful diluents include phosphorus oxychloride, the aromatic acid chloride to be produced, and typical inert solvents such as chlorobenzene, orthodichlorobenzene and l ,2,4-trichlorobenzene.

Still another feature of the invention is that moisture need not be excluded from the reaction system since thionyl chloride efficiently scavenges water, yielding sulfur dioxide and hydrogen chloride (not detrimental to the process). Thus thionyl chloride may be advantageously added to the initial reaction charge where water contamination of the reactants or reactor is suspected or has inadvertently occurred.

EXAMPLES The following examples are intended to illustrate the invention and are not intended to be in limitation thereof.

Other materials and conditions as described above may likewise be employed with advantageous results.

Quantities are in parts by weight unless otherwise stated; the temperatures in C.

Example 1 Sulfur Dioxide Benzal chloride (48.3 grams, 0.3 mole) was charged to a 240 ml capacity shaker bomb lined with Hastelloy C, a corrosion resistant nickel alloy, and equipped with means for sensing internal reaction mass temperatures and free space pressures. The bomb was evacuated, cooled somewhat and sulfur dioxide (32 grams, 0.5 mole) was added, the quantity used corresponding to a 1.67/1 SO /C H CHCl mole ratio. The reactor was sealed, heated to 240 in about 0.5 hour and held at 240 for six hours, during which time the autogeneous pressure ranged from an initial 850 psig to a terminal 2l00 psig. The bomb was cooled to about 25, vented to expel and recover HCl and unreacted S0 and the residual mass distilled to obtain benzoyl chloride in about 85 percent yield; b.p. lOl .0-l02.5/40 mm. Example 2 S0 and O 2,6-Dichlorobenzal chloride (69 grams, 0.3 mole) and sulfur dioxide (64 grams, one mole) were added to the shaker bomb reactor of Example 1. With the reactor cooled to oxygen gas (2.4 grams, 0.075 mole or 0.25 mole/mole dichlorobenzal chloride) was admitted, giving a pressure of 200 psig at 80. The reactor was heated at 240 for six hours, then worked up as in Example 1 to yield six grams of 2,6-dichlorobenzoyl chloride, b.p. l2l129/l5 mm.

Example 3 SO /SOCL and 0 Example 2 was repeated using 0.3 mole S0 and 0.5 mole SOCl The reaction mixture was heated at 230 C. for eight hours and worked up as in Example 1 to give 21 grams of 2,6-dichlorobenzoyl chloride and a small amount of 1,2,3-trichlorobenzene.

When the same reaction is conducted without oxygen, 1,2,3-trichlorobenzene predominates over 2,6- dichlorobenzoyl chloride in the reaction product. Examples 4 to 6 a,a-Dichloro-meta-toluyl chloride (0.3 mole, designated DCFC below) was heated in three separate runs in the reactor of Example 1 with sulfur dioxide (1.0 mole or 3.33 mole/mole DCIC) and (a) without added oxygen, (b) with oxygen (0.075 mole or 0.25 mole/mole DCTC), added at 80 as in Example 2, and (c) with both added thionyl chloride (0.3 mole, or 0.3 mole/mole S0 and oxygen gas as in (b). The reaction mixtures were held at 240 for four hours and worked up by distillation under reduced pressures to yield isophthaloyl chloride, b.p. 145 at 15 mm of Hg pressure. The results are summarized below.

isophthaloyl Ex. Conditions Chloride Yield,

4 S02 alone 20 s so 0 so 6 so 0 socl Example 7 A 70/30 weight percent mixture of a,a,a',a-tetrachloro-meta-xylene and a,a,a',a,a-pentachlorometa-xylene, obtained as by-product in the side chain perchlorination of meta-xylene, was heated at 245 for five hours with three parts S0 per part mixture (corresponding to 12 moles S0 per mole mixture or 6 moles S0 per chlorinated side chain methyl group) and 0.1 part oxygen per part mixture (or about 0.25 mole per CHCl group). The yield of isophthaloyl chloride, recovered by distillation at reduced pressure, was substantially quantitative.

Example 8 SOCl The Example 1 procedure was repeated with thionyl chloride (0.3 mole) in place of sulfur dioxide as the reactant. Benzoyl chloride was obtained in high yield. Example 9 The Example 1 procedure was repeated with 67 parts (0.3 mole) of a,a-dichloro-m-toluyl chloride and 54 parts (0.45 mole) of thionyl chloride. The mixture was heated at 240 for four hours, then distilled under reduced pressure to recover, as forerun, a mixture of SOCl and S Cl and 64 grams of organic distillate analyzing 29 percent a,a,a-trichloro-m-toluyl chloride, 26 percent isophthaloyl chloride and 45 percent unreacted a,a-dichloro-m-toluyl chloride. This product mixture was again heated with 36 parts (0.3 mole) SOC1 for four hours at 240. The resulting product, 58

parts distilled, contained 40 percent a,a,a-trichloro-mtoluyl chloride, about 60% isophthaloyl chloride, b.p. 130135 at 13 mm Hg pressure, and practically nil a,a-dichloro-m-toluyl chloride.

As seen from the foregoing description and examples, the subject invention provides a novel, commercially attractive process for converting aromatic CHC1 groups to COCl groups.

The foregoing detailed description has been given for cleamess of understanding only, and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Process for preparing aromatic acid chlorides which comprises heating (a) an aromatic compound having one or more dichloromethyl groups bonded to aromatic carbon atoms, the substituents on the other aromatic carbon atoms being selected from hydrogen, fluorine, chlorine and carbonyl chloride, all carboncontaining substituents being non-ortho to each other, with (b) a sulfur reactant selected from sulfur dioxide, thionyl chloride and mixtures thereof at a temperature of 200 to 300 C. and at a pressure and of at least 200 psig and for a time sufiicient to convert at least one dichloromethyl group to a carbonyl chloride group.

2. Claim 1 wherein the sulfur reactant is present in the amount of from one to about moles per dichloro-methyl group.

3. Claim 2 wherein the sulfur reactant is a mixture of sulfur dioxide and thionyl chloride, the molar ratio of 4. Claim 3 wherein the molar ratio is in the range of 0.2:1 to 1:1.

5. Claim 2 wherein there is also initially present about 0.1-0.5 molecules of molecular oxygen per dichloro-methyl group.

6. Claim 5 wherein the aromatic compound is a benzal chloride having one to two substituents individually selected from dichloromethyl and carbonyl chloride groups attached to ring positions non-ortho to each other and to the benzal chloride dichloromethyl group and zero to three ring chloro groups.

7. Claim 6 wherein the sulfur reactant is sulfur dioxide.

8. Process for preparing benzoyl chlorides which comprises heating (a) a benzal chloride having zero to two ring chloro groups and one ring substituent nonadjacent to the dichloromethyl group of the benzal chloride selected from dichloromethyl and carbonyl chloride groups with (b) 1.1 to five molecules, per dichloromethyl group, of a sulfur reactant selected from sulfur dioxide, thionyl chloride and mixtures thereof and (c) 0.2 to 0.4 molecules, per dichloromethyl group, of molecular oxygen at 200 to 300 C. and a pressure of at least 200 p.s.i.g. for a time suflicient to convert at least one dichloromethyl group to a carbonyl chloride group.

9. Process for preparing isophthaloyl chloride which comprises heating (a) a benzal chloride selected from I f I I a a a -tetr chloro-ml ne 0: a q -pentac oro-m-xy ene, ragao oro-m-toluficl ldnde or mixtures of any two or more thereof with (b) sulfur dioxide and molecular oxygen at a temperature in the range of 200-300 C. and pressure of at least 200 psig and for a time sufficient to convert all substituents to thionyl chloridecsulfur dioxide being about in the range Carbonyl chlofide groupsofO.1lto 2:1. 

2. Claim 1 wherein the sulfur reactant is present in the amount of from one to about 10 moles per dichloro-methyl group.
 3. Claim 2 wherein the sulfur reactant is a mixture of sulfur dioxide and thionyl chloride, the Molar ratio of thionyl chloride:sulfur dioxide being about in the range of 0.11 to 2:1.
 4. Claim 3 wherein the molar ratio is in the range of 0.2:1 to 1:1.
 5. Claim 2 wherein there is also initially present about 0.1-0.5 molecules of molecular oxygen per dichloro-methyl group.
 6. Claim 5 wherein the aromatic compound is a benzal chloride having one to two substituents individually selected from dichloromethyl and carbonyl chloride groups attached to ring positions non-ortho to each other and to the benzal chloride dichloromethyl group and zero to three ring chloro groups.
 7. Claim 6 wherein the sulfur reactant is sulfur dioxide.
 8. Process for preparing benzoyl chlorides which comprises heating (a) a benzal chloride having zero to two ring chloro groups and one ring substituent nonadjacent to the dichloromethyl group of the benzal chloride selected from dichloromethyl and carbonyl chloride groups with (b) 1.1 to five molecules, per dichloromethyl group, of a sulfur reactant selected from sulfur dioxide, thionyl chloride and mixtures thereof and (c) 0.2 to 0.4 molecules, per dichloromethyl group, of molecular oxygen at 200* to 300* C. and a pressure of at least 200 p.s.i.g. for a time sufficient to convert at least one dichloromethyl group to a carbonyl chloride group.
 9. Process for preparing isophthaloyl chloride which comprises heating (a) a benzal chloride selected from Alpha , Alpha , Alpha '', Alpha ''-tetrachloro-m-xylene, Alpha , Alpha , Alpha , Alpha '', Alpha ''-pentachloro-m-xylene, Alpha , Alpha -dichloro-m-toluyl chloride or mixtures of any two or more thereof with (b) sulfur dioxide and molecular oxygen at a temperature in the range of 200*-300* C. and pressure of at least 200 psig and for a time sufficient to convert all substituents to carbonyl chloride groups. 